ERBB3 and breast cancer: Both T-DM1 and RC48 are effective in treating patients with HER2-positive BC who progress to taxanes, which, similar to DM1 and MMAE, act through microtubule disruption.2,10 Patritumab Deruxtecan, a HER3 ADC that carried the same payload as T-Dxd, might remain sensitive in patients who progress on T-Dxd with decreased HER2 expression.25 Thus, it is conceivable that the strategy using a similar chemotherapeutic agent may allow for continued antitumor activity.